So a Flintlock Pistol in 5e D&D deals 1d10 damage. A longsword deals 1d8 damage, 1d10 if you hold it with both hands.
But if you've ever seen what a sword can -do- to a human body, you know that the damage difference is incomparable!
Yeah, a bullet can be really effective at killing a person by catastrophically randomizing a narrow line through their body. If you hit something vital, death is assured in fairly short order, and if you don't hit something vital there's a decent shot the person will still bleed out over the course of the next hour or two, depending on their activity during that time and lack of medical care.
If you hit something vital with a sword, your target will -also- die in very short order. But if you don't strike something vital they will STILL DIE IN VERY SHORT ORDER. This is because a Sword catastrophically randomizes a very large area of the human body on each strike. At least when compared to something like a Pistol.
Depending on your ammo type a gun is going to put a fairly small hole in the front of your target and a moderately larger hole out of the back of your target with a relatively straight line between the two. With the appropriate training, a sword will completely eradicate your ability to have intestines that remain both inside your body and intact.
Take a look at this video if you can/care to (TW: Dead Animal, Fake Blood, Violence)
This is a Kilij. Roughly the same shape as a scimitar, it's got a slightly weighted tip to increase percussive force. It would not be out of place in most D&D campaign settings. It cuts -through- that pig on the first strike. And the second. The third sets it spinning and the fourth cuts through, again.
Compare that to a single hole running through your torso.
You could of course argue that that was a fairly small pig and thus the sword could easily pass through it. But upscale that pig and the damage would -still- be significant even if the sword didn't manage to pass through the bones. And all the internal organs in it's very wide, very deep, path would be randomized and compromised.
Now I'm not saying that pistols aren't deadly. They flatly and -absolutely- are deadly. But compared to the damage that a -sword- can do? It's not even in the same ball park. And that's not even getting INTO things like two-handed swords, axes of any variety, or spears...
Now you could argue that they do so much damage because HP is an abstraction and it shows how well they punch through armor... but you still make the same attack roll with the same bonuses and the same AC to overcome. And AC is -itself- an abstraction accounting for both the deflecting and cushioning effects of a piece of armor between you and oncoming metal.
And it only gets worse when you get into Revolvers and Rifles that jump up to the 2d8 and 2d10 damage range.
All things considered... I just feel like guns should do damage in-line with the rest of the weapons available. 1d6 for a pistol, 1d10 for a rifle. Basically a Hand and Heavy Crossbow for all intents and purposes. And then making them repeating weapons or whatever should just increase the number of shots before you have to spend an action reloading. I think the designers, and many players, overwhelmingly inflate just how much damage a gun does to a human being compared to the weapons, and monsters, D&D characters face.
That's my take, anyhow.